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Methane levels at a multimillion-dollar Otay Ranch housing project dropped by more than 50 percent during a recent six-month period, according to a new report, but the source of the gas has yet to be found.

Methane, a colorless, odorless and highly flammable gas, can pose health and safety risks, particularly in housing developments when left unmitigated.

During construction last year of the 450-acre Village of Escaya, methane and other volatile chemicals were found in the soil. The Otay Water District briefly withheld water meters from the project until developer HomeFed Corp. provided testing results that showed the methane levels would not damage the district’s pipes.

Homebuyers started moving in to their new homes in the eastern Chula Vista development in January.

The new report by HomeFed consultant TRC, a construction and management firm, compares methane levels measured in January on the Escaya property to those taken in June and July 2017.

The January tests showed nine lots have high enough levels of the gas to warrant further testing. Of those, five tested high enough to consider methane controls.

Even though it’s not required, HomeFed will install a vapor barrier beneath the foundation of every home at Escaya, company Vice President Kent Aden told inewsource this week.

“There’s a lot of people in this project that are getting it that don’t need it, but you could argue that you don’t know what’s going to happen in the future,” Aden said. “These people are good no matter what comes up.”

The January test results, which the county recently made public, show no methane was found on a 10-acre lot where the Chula Vista Elementary School District plans to build a school in Escaya.

The district will start doing its own tests at the site within the next six months, district spokesman Anthony Millican said Thursday. If all goes well, the site could be purchased by the end of 2019.

“The timeline is fluid but we are dedicated to opening a school in the community in July 2021,” Millican said in an email.

The county Department of Environmental Health and HomeFed will use the testing data to figure out next steps, including continuing to try to locate the source of the methane, HomeFed officials said.

A trash truck drives to the Otay Landfill near Main Street and Maxwell Road in Chula Vista on July 16, 2018. (Megan Wood/inewsource)

The nearby Otay Landfill has been previously cited as a potential cause for the higher methane levels.

The January report said the highest concentrations of methane at shallow depths were found in lots adjacent to the dump.

Republic Services, manager of the Otay Landfill, declined an inewsource request for an interview. The company said in a statement it is complying with all regulatory rules and has not been asked by any agency to change its operations.